The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device which prevents stripping or corrosion of a wiring layer formed on a peripheral portion of an insulative substrate.
FIG. 1 is a schematic block diagram of a conventional active matrix type liquid crystal display device. The pixel portion (display panel) 101 comprises a plurality of scanning lines (gate wiring) G1-Gm, a plurality of data lines (drain wiring) D1-Dm crossing orthogonally with the gate wiring G1-Gm, and pixels 102 provided at each of the intersections of the gate wirings and the drain wirings. A gate signal (a scanning signal) from a gate driver 103 is applied to the gate wirings G1-Gm. A data signal (a video signal) from a drain driver (data driver ) 104 is applied to the drain wirings D1-Dm. The gate and drain drivers 103 and 104 form a peripheral driver circuit 105. A liquid crystal display device which comprises the driver 103 or 104 and the pixel portion 101 formed on an insulative substrate 11 (FIG. 3) is generally called a driver built-in liquid crystal display device. The gate driver 103 may be provided on both sides of the pixel portion 101. The drain driver 104 may be provided on both sides of the pixel portion 101.
FIG. 2 is an equivalent circuit diagram of one of the pixels 102. The pixel 102 comprise an TFT (Thin Film Transistor) 106 as a pixel drive element, a liquid crystal cell LC and a supplementary capacitor (a storage capacitor or an additional capacitor) SC. The gate wiring Gn is connected to the gate of the TFT 106, and the drain wiring Dn is connected to the drain of TFT 106. The source of the TFT 106 is connected to the supplementary capacitor SC and a display electrode (pixel electrode) 107 of the liquid crystal cell LC. The liquid crystal cell LC and the supplementary capacitor SC form a signal storage element. An opposite electrode (common electrode) 108, which is arranged opposite to the display electrode 107 of the liquid crystal cell LC, receives a voltage Vcom. The supplementary capacitor SC comprises a storage electrode 109 connected to the source of the TFT 106 and a supplementary capacitor electrode 110 to which a constant voltage VR is applied. The opposite electrode 108 of the liquid crystal cell LC is common to all of the pixels 102. Static capacity is formed between the display electrode 107 and the opposite electrode 108. The supplementary capacitor electrode 110 may be alternatively connected to the adjacent gate wiring Gn+1.
FIG. 3 is a partial cross sectional view of the conventional display panel 101. A liquid crystal layer 13 is provided between opposing first and second insulative substrates 11 and 12 which are preferably made of transparent glass material. An aluminum alloy film 14 which forms a wiring layer, a planarizing insulation film 15 preferably made of acrylic resin and an orientation film 16 preferably made of polyimide resin are laminated on the first substrate 11. An opposite electrode 17 (i.e., the opposite electrode 108) preferably made of ITO (Indium Tin oxide) and a second orientation film 18 preferably made of polyimide resin are laminated on the second substrate 12. A sealing material 19 preferably an epoxy resin is provided between the insulative substrates 11 and 12 to prevent leakage of the liquid crystal layer 13. Specifically, the sealing material 19 is provided between the orientation films 16 and 18 at the peripheral portions of the substrates 11 and 12.
On the peripheral portions of the insulative substrates 11 and 12 to which the sealing material 19 is provided, the aluminum alloy film 14 is formed all over the first insulative substrate 11. Adhesion strength of the aluminum alloy film 14 to the planarizing insulation film 15 is lower than that of the planarizing insulation film 15 to the insulative substrate 11. Therefore, the planarizing insulation film 15 may easily peel off the aluminum alloy film 14.
FIG. 4 is a partial cross sectional view of a second conventional liquid crystal display device in which the aluminum alloy film 14 is formed as a lead wiring on the peripheral portion of the insulative substrate 11. The sealing material 19 is formed between the opposite electrode 17 and the planarizing insulation film 15 to enclose liquid crystal layer 13 and the orientation films 16 and 18 at the peripheral portions of the insulative substrates 11 and 12.
A portion of the aluminum alloy film 14 forms a contact pad 20. The contact pad 20 may be made of a different material from the aluminum alloy film 14. The opposite electrode 17 is formed to extend to the edge of the substrate 12, and an extended portion of the opposite electrode 17 is connected to the contact pad 20 via a conductive material 21. The conductive material 21 is preferably made of resin mixed with conductive material. The contact pad 20 receives a voltage Vcom via the input terminal (not shown) of the lead wiring of the aluminum alloy film 14. The voltage Vcom is applied to the opposite electrode 17 via the conductive material 21.
Various input terminals (a power supply input terminal of voltage Vcom or VR, a power supply input terminal of the peripheral drive circuit 105 and an input terminal of the data signal) are concentrated on the lead wiring of the aluminum alloy film 14. The arrangement of the input terminals facilitates drawing wirings of an equipment when the liquid crystal display device is mounted into various apparatus, such as a personal computer, a word processor, an electronic notebook, or a television display monitor.
The area of the contact pad 20 provided on the peripheral portion of the insulative substrate 11 is larger than the area necessary to connect the liquid crystal display device with an external circuit and is exposed out of the peripheral portion of the substrate 11. If the exposed portion of the contact pad 20 is exposed to air, it may cause corrosion of the aluminum alloy film 14 of the contact pad 20. Moreover, moisture or contaminants in the air may penetrate between the contact pad 20 and the conductive material 21, adversely affecting the liquid crystal layer 13 and the TFT 106.
It is an object of the present invention to provide a liquid crystal display device which prevents stripping of the insulation film from the wring layer.
It is a secondary object of the present invention to provide a liquid crystal display device which prevents corrosion of the wiring layer and penetration of moisture or contaminants.